1. Field of the Disclosure
The disclosure generally relates to a method of treating a biological composition for use in its downstream conversion to a biofuel and, more specifically, to a method of removing one or more contaminants from a contaminant-containing biological composition that includes animal fats and plant oils.
2. Brief Description of Related Technology
Biomass is a renewable alternative to fossil raw materials in production of liquid fuels (e.g., biofuels) and chemicals. Increase of biofuels production is part of the government's strategy to improve energy security and reduce green house gas emissions. However, most biomass has high oxygen content which lowers fuel quality and heat value. Upgrading biomass or biomass intermediates into high quality hydrocarbon fuels thus requires removal of oxygen. The biomass oxygen may be in the form of an ester, carboxylic acid, or hydroxyl groups. Removal of oxygen by catalytic reaction with hydrogen is referred to as hydrodeoxygenation (HDO). This reaction may be conducted with conventional fixed-bed, bimetallic, hydrotreating catalysts, such as sulfided nickel-molybdenum (NiMo) or cobalt-molybdenum (CoMo), which are commonly used in refineries.
Unrefined plant oils (e.g., vegetable oils) and animal fats have undesirable quantities of phosphorus in the form of phospholipids and other contaminants, including metals. In addition, animal fats may contain significant amounts of metal salts (e.g., metal chloride salts), which are sufficiently soluble in the fat/grease feeds, but undesirably may precipitate during the HDO reaction and may plug the catalyst bed. The metals/salts can also deactivate the catalyst by reducing available pore surface to accomplish efficient chemical reactions. In the presence of free fatty acids, salts like metal chlorides may form soluble soaps (e.g. calcium stearate). In such form, metals are difficult to remove using conventional cleanup technologies such as water washing.
Several prior art processes for producing fuels from starting materials such as plant oils and animal fats are known. Conversion of vegetable oils to n-paraffins has been reported in the prior art. Some prior art has shown that the process may be applied to other forms of biomass such as tall oil fatty acids, animal fats, and restaurant greases. Hydroisomerization of the bio-derived n-paraffins to isoparaffinic diesel has been taught in the prior art. Other prior art describes use of feed treatment upstream of an HDO reactor. See generally, U.S. Pat. No. 8,026,401, the disclosure of which is incorporated herein by reference.
As described in US-2009-0314688 A1, the disclosure of which is incorporated herein by reference, when producing biodiesel from crude oils, it is highly desirable to reduce the phosphorus content to at most 20 parts per million (ppm) in oil, grease, fat or tallow feedstock to ensure that the final product meets governmental regulatory standards on diesel engine exhaust emission. Oil refining procedures depend on the type of oil and its composition and usually consist of degumming, alkali neutralization, bleaching and deodorization. Degumming refers to the removal of phosphatides and other similar compounds by adding water and/or acid to oil and centrifuging. The main purpose of the degumming is to remove phosphorus, which is present in the crude oil in the form of hydratable phosphatides and non-hydratable phosphatides. Without efficient removal of the phosphatides, the downstream refining processes may not deliver acceptable results. In addition to the removal of non-hydratable phosphatides, the removal of iron and other metals and salts thereof is highly desirable. Thereafter, the oil can be bleached, dewaxed, hydrogenated, and/or deodorized to produce a more stable product.
A number of degumming methods are known in this art, including water degumming (treatment of crude oil with hot water); acid degumming (treatment of crude oil with phosphoric acid or citric acid); acid refining (treatment of water-degummed oil with an acid, which is then partially neutralized with alkali and centrifuged to remove residual gums and free fatty acids); dry degumming (acid degumming with very small amount of water, combined with bleaching); enzymatic degumming (modification of phospholipids with enzymes to obtain the water-soluble compounds); degumming with help of chelating agents (EDTA-ethylenediaminetetraacetic acid, aspartic amino acid, organic malic and fumaric acids, etc.); and membrane/ultra filtration degumming (passage of crude oil through a semi permeable membrane impermeable to phospholipids).
US-2010-0056833 A1, the disclosure of which is incorporated herein by reference, describes a process that attempts to address the aforementioned problems of gumming and contaminant removal from a composition that contains both animal fats and plant oils. The inventors here have discovered improvements on the teachings set forth in this publication.